The fire is believed to have started with lubricating oil in a storage tanker. Fire crews were dispatched at about 8 p.m., and the fire was under control in less than two hours, said Middletown deputy fire chief Brent Dominy.

"There were no injuries and the company does not anticipate any impact to the plant's operation," Mike Wallner, spokesman for the West Chester-based company, said in a statement.

He said the cause of the fire was still being investigated.

The air "was nasty," resident Mike Slusher said. He lives across the street from the plant.

"You could taste it," he said. "I wouldn't let my dog outside."

Police blocked an intersection near the plant, and some motorists pulled over and watched the flames.